One of the most dangerous machines from the standpoint of serious accidental injury to the operator is the band saw. The ever present menace of the moving sharp teeth is aggravated by the high speed operation of the saw employed in industrial and commercial activities in order to maximize the efficiency of the operation. Even the slightest touching by a finger, movement or other body part results in serious injury. Even the realization of a close call is an enervating experience, frequently necessitating a recess for recovery from the shock caused by the knowledge and continuing fear of the consequences of an accident.
The use of a guard in front of the otherwise exposed length of the band saw is standard safety practice. When workpieces which are flat and of substantially uniform thickness are being cut, the provision of a guard presents no particular problem. It may be vertically adjustable for a particular job to allow passage of the workpiece under the bottom extremity of the guard with sufficient tolerance to avoid interference with the operation without leaving space for the entry of, for example, a finger. On the other hand, very difficult safety problems are posed in the sawing of workpieces which are uneven, varying in height above the saw table along the line of cut. A fixed guard must be high enough to permit the highest part of the workpiece to pass under it, leaving the dangerous exposed blade at lower levels of the workpiece at the cut.
The invention herein described provides a commercially practical solution to the hazards of cutting uneven workpieces with a band saw.
The primary object of the invention is to provide a band saw safety guard which automatically moves up and down responsive to the contour of the top surface of the workpiece; that is, the elevation of the guard changes continuously with the height of the workpiece in the vicinity of the part being cut so that the saw band that would otherwise be exposed above the workpiece while cutting lower levels is covered by the guard at all times during the cutting operation.
This object is achieved by arranging a vertically movable guard operated by a pneumatic system which, in turn, is controlled by a cam follower mounted at the bottom extremity of the guard to ride upon and respond to the changing elevational contours of the workpiece as it is moved by the operator into the saw. The top surface of the workpiece acts as a cam driving the follower in vertical movement which controls a valve of the pneumatic system, causing the guard to be elevated or lowered to reflect the instantaneous level of the workpiece at the cut.
A subsidiary object is to provide a guard control system having two aspects of guard movement, one being the normal up and down movement at response speeds adjusted to the particular job, the other being a very rapid lifting of the guard to meet extraordinary conditions such as a very steep workpiece incline approaching the blade or to provide restricted manual control.
A general object is to provide a band saw guard which provides maximum safety while causing minimum interference with the sawing operation; also to provide such a safety guard which is adjustable to adapt the band saw machine to a wide variety of sawing operations.
A further object is to provide safety features designed to protect the operator from a variety of possible hazards in the use of the band saw machine without unduly interfering with the efficient use of the machine.